This invention relates to an acoustic surface wave resonator device and, more particularly, an acoustic surface wave resonator device which has a specific lead terminal connection and wiring structure to allow both in phase and out of phase operations.
In the fields of communications and among other categories of electrical equipment, demands have arisen for filters or oscillating frequency controllers having very narrow frequency response characters. U.S. Pat. No. 3,886,504 discloses one technique responding to these demands. According to this patent, as shown in FIG. 1, two sets of interdigital electrodes each consisting of a pair of interleaving comb-shaped electrodes 2, and two acoustic surface wave (SAW) reflectors 3 sandwiching them are arranged on a piezoelectric substrate 1.
An oscillator using such a SAW resonator 11 has the configuration as shown in FIG. 2. In the oscillator shown in FIG. 2, a SAW resonator 11 having a high Q factor is connected to an amplifier 12 to form a feedback loop and oscillates at a frequency satisfying: EQU Gamp+Gres.gtoreq.1 . . . .circle.A EQU .PHI.amp+.PHI.res=2n.pi. . . . .circle.B
where Gamp and Gres are gains of the amplifier 12 and the SAW resonator 11, respectively, Gres being smaller than unity, and .PHI.amp and .PHI.res are phase shifts of the amplifier 12 and the SAW resonator 11, respectively. In this case, in accordance with the circuit configuration, the amplifier 12 is classified into in phase type (.PHI.amp.perspectiveto.2n.pi.) and out of phase type (.PHI.amp.perspectiveto.(2n+1).pi.). For this reason, in accordance with the amplifier 12, the SAW resonator 11 must be of in phase type (.PHI.res.perspectiveto.2n.pi.) and out of phase type (.PHI.res.perspectiveto.(2n+1).pi.).
FIG. 3 shows the frequency characteristics of the SAW resonator shown in FIG. 2.
Referring to FIG. 3, curve 21 shows amplitude characteristics, curve 22 shows phase characteristics of a SAW resonator of out of phase type, and curve 23 shows phase characteristics of a SAW resonator of in phase type. Note that the curves 22 and 23 show the same characteristics except that they are out of phase.
In a SAW resonator, the phases of input/output electrodes are mainly determined in accordance with the relative positions of fingers of the two sets of comb-shaped electrodes. FIG. 4 shows a state wherein a standing wave 32 is generated on a piezoelectric substrate 30 at a frequency in the vicinity of the resonance frequency of the SAW resonator. Referring to FIG. 4, electrical signals at terminals 33 and 35 are substantially in phase, and phase shifts between are of in phase type. However, phase shifts between terminals 33 and 36 are of out of phase type. When the distance between the centers of fingers of the two sets of comb-shaped electrodes connected to terminals as input/output terminals of electrical signals is an n multiple of an acoustic surface wavelength .lambda. at the resonance frequency, phase shifts are of in phase type. However, when this distance is (n+1/2) the wavelength .lambda., phase shifts are of out of phase type. Reference numerals 37 and 38 denote fingers of the interdigital electrodes.
In consideration of the above, when SAW resonators of in phase type and out of phase type are actually realized, the following structure is adopted:
The first structure will be described with reference to FIGS. 5(a) and 5(b). A SAW resonator shown in FIG. 5(a) is of in phase type wherein three lead terminals, e.g., lead pins 51 are formed, and bonding pads at the signal sides of interdigital electrodes 53 are formed at one side of a stem 52. A SAW resonator shown in FIG. 5(b) is of out of phase type wherein the relative positions of the two signal output fingers are shifted by .lambda./2 from that shown in FIG. 5(a). Therefore, the first structure requires two types of SAW resonators. For this reason when SAW resonators are formed by patterning, two types of glass masks for photoetching are required for in phase type and out of phase type. This complicates the manufacturing process, resulting in inconvenience. Reference numeral 54 denotes a glass member for mounting each lead pin 51 on the stem 52.
The second structure will be described with reference to FIGS. 6(a) and 6(b). In accordance with this structure, two types of SAW resonators are manufactured using SAW resonators 61 of the same type but adopting different bonding positions. Although this second structure does not require the use of two types of SAW resonators, two different bonding procedures must be followed for in phase type and out of phase type SAW resonators.
Common problems with the first and second structures result in the manufacturing process becoming complex and a user must use two types of SAW resonators for assembling an oscillator using SAW resonators of these structures. When mass-production is necessary, since a single SAW resonator cannot be operated as either an in phase or out of phase type SAW resonator, a user must specify the particular type when ordering SAW resonators from a factory. This makes the designing of oscillators difficult.